As part of the first Concept Battle, here is my entry... There may be some typos in it because I'm posting that when I shouldn't have that much time... Ability that fulfill the challenge is W. Icons will come when I'll have some more proper time.

Astral Burn

Each of Celeste's damaging abilities apply a stack of Astral Burn to enemy units for 3 seconds, up to a maximum of 5 stacks. Each stack reduces the magic resistance of the affected unit by 3% and increases Celeste's by that much.

Collapse

RANGE: 850

COST: 70 / 75 / 80 / 85 / 90 mana

COOLDOWN: 13 / 12 / 11 / 10 / 9

Active:Celeste causes energy to collapse on the target area, dealing magic damage in a 250 radius area after a 0.5 second delay.

Damage: 40 / 65 / 90 / 115 / 140 (+ 35% AP)

1 second thereafter, the energy collapses again on the same area, dealing magic damage.

Total Damage: 80 / 130 / 180 / 230 / 280 (+ 70% AP)

Cosmic Link

RANGE: 1050

COST: 70 / 75 / 80 / 85 / 90 mana

COOLDOWN: 16 / 15 / 14 / 13 / 12

Active:Celeste fires out a burst of energy in a line, dealing magic damage to the first enemy struck.

Damage: 30 / 50 / 70 / 90 / 110 (+ 25% AP)

After Cosmic Link hits an enemy, the burst of energy continues through for 300 units, searching for secondary targets. If it hits a second enemy, it deals magic damage to the second unit as well and form a 350 units tether between both targets for 4 seconds, revealing them. If the tether is broken early, both targets take magic damage again and are stunned for a short duration.

First Cast:Celeste calls down a beam of stellar energy to a target location after a 0.625 delay that lasts for 5 seconds. Enemies within 100 range of the beam take high magic damage per second, while enemies within 250 range take lesser magic damage per second. Damaged enemies are also slowed by 20% for 1 second, decaying when not taking damage from the beam.

Damage per second (Inner): 80 / 140 / 200 (+40% AP)

Damage per second (Outer): 40 / 60 / 80 (+15% AP)

Max Damage (Inner): 400 / 700 / 1000 (+200% AP)

Max Damage (Outer): 200 / 300 / 400 (+75% AP)

Second Cast:Celeste directs the beam toward the mouse cursor with a speed of 300. Once the beam damages an enemy champion, it will automatically follow them until the enemy champion dies or escapes it.